1. Field of the Invention
The invention relates generally to liquefaction and demulsification agents for hydrocarbon based oil sludges and to their use to facilitate the demulsification and liquefaction of hydrocarbon based oil sludges and more particularly to their use to facilitate the demulsification and liquefaction of sludges in storage tanks.
2. Prior Art
Hydrocarbon based oils such as petroleum oils or vegetable oils are often stored in tanks. Over time, `sludge` forms in the bottom of these tanks. Sludge is a mixture of deposits that collect at the bottom of the tanks. The sludge can be distinguished from oil in the tank primarily by a difference in viscosity. The minimum viscosity for a sludge varies within the industry from as low as 100 centipoise to as high as 500 centipoise.
The composition of the sludge varies from tank to tank and will depend upon the composition of the oil or oils that have been stored in a particular tank. The components of the sludge can generally be broken into three groups: water and water soluble materials (waters); oils and oil soluble materials (oils); and solids. The solids generally become wetted with either oils or waters. The sludge is formed when these components emulsify. (The more technically correct term for a solid/liquid colloid is "sol." However, for the sake of convenience, emulsion is used herein to refer to both liquid/liquid and to solid/liquid colloids)
Over time, the heavier elements in the oil such as paraffins, asphaltenes and solids migrate to the bottom of the tank and enter the sludge. As the concentration in the sludge of these heavier components increases, the sludge becomes more viscous and, depending upon the sludge components, may even solidify. The sludge becomes problematic when its viscosity prevents it from being pumped, and it begins to build up at the bottom of the tank. Eventually these sludges must be removed. If left unchecked, the sludge formation, will adversely impact the capacity of the tanks. However, removal of these sludges poses an expensive and sometimes dangerous problem for those in the tank farm industry.
In one removal method, these sludges are treated with aromatic compounds such as toluene to dissolve them. These chemicals have several shortcomings. First, the aromatic compounds are generally soluble in oil but not in water. This makes it difficult for the aromatics to effectively liquefy sludge which contain any substantial amount of water. Second, these chemicals are poor demulsifiers, so the liquefied sludge is still an emulsion. Introduction of demulsifiers into the sludges that have been liquefied aromatically has been found to lead to poor results. This is believed to result from the aromatic's inability to form a solution with the waters in the sludge. The failure to effectively place the waters into solution is believed to inhibit the ability of the demulsifiers to interact with the emulsified particles and thus to break the emulsion. Third, these chemicals often have health and safety problems associated with them. Many aromatic compounds are highly flammable and some are known carcinogens. This latter trait can substantially increase the disposal expenses of sludges that have been aromatically liquefied.
In another method, heat is applied to the sludge, usually with steam. This process also provides less than satisfactory results. Some sludges are not readily susceptible to liquefaction through heating. Once liquefied, the sludge must be pumped before it cools because cooling usually results in the reformation of a solid or semi-solid sludge. Cooling in the pump lines can lead to blockages which can be quite difficult to clear. Sludge that is removed using heat is often difficult to remove from the receiving vessel without reheating it. Heating the sludge can also cause some sludges to emit vapors which may create a fire hazard or a health hazard.
A third option is manual removal. This method is time consuming and expensive. The men that work in the tank are exposed to potential health risks connected with the chemicals in the tank as well as to possible injury in the fires or explosions that are a constant concern in the petroleum industry. Despite these drawbacks, manual removal is the only feasible removal mechanism for many sludges. Even when the previously discussed methods are employed, the sludge is often not rendered sufficiently fluid to be pumped out of the tank and at least some portion must be manually removed.
Removal of sludge manually is often very labor intensive, and can take as much as 180 days to clean a single tank. This results in lost revenue to the tank farm due to diminished storage capacity during this period. The labor requirements can often push the cost of cleaning a single tank over $(US) 500,000.00.
All of the previously discussed sludge removal methods share a common shortcoming: the loss of commercially valuable hydrocarbons contained in the sludge. The oils that are trapped in the sludge often have commercial value, but because of their emulsified state, it is not feasible to refine them. Consequently, these sludges must be discarded. This results in a double loss to the tank farm operator. First, he must throw away the unusable hydrocarbons trapped in the sludge. Second, the sludge is frequently treated as hazardous waste and can be expensive to dispose.
Accordingly, a demulsifier, a liquefaction agent, and method for using the same are desired to meet the following objectives.